This application relates to a circuit and method of detecting a fault on a transformer-rectifier unit.
Modern electrical systems are becoming more and more complex. One system involves a variable frequency generator that supplies a variable AC current to a bus. The AC current may pass through a transformer-rectifier unit to convert the AC electric power to DC electric power.
The transformer-rectifier unit DC output may typically have voltage ripples that contain higher harmonics of the AC electric power frequency, along with noise induced by loads on the DC bus.
Harmonics are voltages or currents that operate at a frequency that is an integer of a fundamental frequency. Thus, if the frequency of the power signal is X, then the second harmonic frequency would be 2X.
At times, a transformer-rectifier unit may have a fault. In such cases, a voltage ripple that is the second harmonic of the frequency of the AC bus supplied to the transformer-rectifier unit will be present.
Thus, for fault detection, it is known to look for the presence of a second harmonic of the AC frequency. However, this second harmonic must be detected in the presence of other frequencies to reliably indicate a fault on the transformer-rectifier unit. Detection of a given harmonic is complicated because the generator AC power is not constant frequency, but may vary over a two to three times range.
Such systems are often utilized on aircraft applications.